Periodic Table > Molybdenum
 

Glossary


Allotropes
Some elements exist in several different structural forms, called allotropes. Each allotrope has different physical properties.


For more information on the Visual Elements image see the Uses and properties section below.

 

Glossary


Group
A vertical column in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.


Period
A horizontal row in the periodic table. The atomic number of each element increases by one, reading from left to right.


Block
Elements are organised into blocks by the orbital type in which the outer electrons are found. These blocks are named for the characteristic spectra they produce: sharp (s), principal (p), diffuse (d), and fundamental (f).


Atomic number
The number of protons in an atom.


Electron configuration
The arrangements of electrons above the last (closed shell) noble gas.


Melting point
The temperature at which the solid–liquid phase change occurs.


Boiling point
The temperature at which the liquid–gas phase change occurs.


Sublimation
The transition of a substance directly from the solid to the gas phase without passing through a liquid phase.


Density (g cm−3)
Density is the mass of a substance that would fill 1 cm3 at room temperature.


Relative atomic mass
The mass of an atom relative to that of carbon-12. This is approximately the sum of the number of protons and neutrons in the nucleus. Where more than one isotope exists, the value given is the abundance weighted average.


Isotopes
Atoms of the same element with different numbers of neutrons.


CAS number
The Chemical Abstracts Service registry number is a unique identifier of a particular chemical, designed to prevent confusion arising from different languages and naming systems.


Fact box

 
Group Melting point 2622°C, 4752°F, 2895 K 
Period Boiling point 4639°C, 8382°F, 4912 K 
Block Density (g cm−3) 10.2 
Atomic number 42  Relative atomic mass 95.95  
State at 20°C Solid  Key isotopes 95Mo, 96Mo, 98Mo 
Electron configuration [Kr] 4d55s1  CAS number 7439-98-7 
ChemSpider ID 22374 ChemSpider is a free chemical structure database
 

Glossary


Image explanation

Murray Robertson is the artist behind the images which make up Visual Elements. This is where the artist explains his interpretation of the element and the science behind the picture.


Appearance

The description of the element in its natural form.


Biological role

The role of the element in humans, animals and plants.


Natural abundance

Where the element is most commonly found in nature, and how it is sourced commercially.

Uses and properties

 
Image explanation
The image is of a valve wheel, reflecting the use of molybdenum alloys in valves and boilers.
Appearance
A shiny, silvery metal.
Uses
Molybdenum has a very high melting point so it is produced and sold as a grey powder. Many molybdenum items are formed by compressing the powder at a very high pressure.

Most molybdenum is used to make alloys. It is used in steel alloys to increase strength, hardness, electrical conductivity and resistance to corrosion and wear. These ‘moly steel’ alloys are used in parts of engines. Other alloys are used in heating elements, drills and saw blades.

Molybdenum disulfide is used as a lubricant additive. Other uses for molybdenum include catalysts for the petroleum industry, inks for circuit boards, pigments and electrodes.
Biological role
Although it is toxic in anything other than small quantities, molybdenum is an essential element for animals and plants.

There are about 50 different enzymes used by plants and animals that contain molybdenum. One of these is nitrogenase, found in nitrogen-fixing bacteria that make nitrogen from the air available to plants. Leguminous plants have root nodules that contain these nitrogen-fixing bacteria.
Natural abundance
The main molybdenum ore is molybdenite (molybdenum disulfide). It is processed by roasting to form molybdenum oxide, and then reducing to the metal. The main mining areas are in the USA, China, Chile and Peru. Some molybdenum is obtained as a by-product of tungsten and copper production. World production is around 200,000 tonnes per year.
 
Glossary

Atomic radius, non-bonded
Half of the distance between two unbonded atoms of the same element when the electrostatic forces are balanced. These values were determined using several different methods.


Covalent radius
Half of the distance between two atoms within a single covalent bond. Values are given for typical oxidation number and coordination.


Electron affinity
The energy released when an electron is added to the neutral atom and a negative ion is formed.


Electronegativity (Pauling scale)
The tendency of an atom to attract electrons towards itself, expressed on a relative scale.


First ionisation energy
The minimum energy required to remove an electron from a neutral atom in its ground state.

Atomic data

 
Atomic radius, non-bonded (Å) 2.17 Covalent radius (Å) 1.46
Electron affinity (kJ mol−1) 72.171 Electronegativity
(Pauling scale)
2.16
Ionisation energies
(kJ mol−1)
 
1st
684.316
2nd
1559.2
3rd
2617.65
4th
4476.9
5th
5257.49
6th
6640.854
7th
12124.734
8th
13855.3
 

Glossary

Data for this section been provided by the British Geological Survey.


Relative supply risk

An integrated supply risk index from 1 (very low risk) to 10 (very high risk). This is calculated by combining the scores for crustal abundance, reserve distribution, production concentration, substitutability, recycling rate and political stability scores.


Crustal abundance (ppm)

The number of atoms of the element per 1 million atoms of the Earth’s crust.


Recycling rate

The percentage of a commodity which is recycled. A higher recycling rate may reduce risk to supply.


Substitutability

The availability of suitable substitutes for a given commodity.
High = substitution not possible or very difficult.
Medium = substitution is possible but there may be an economic and/or performance impact
Low = substitution is possible with little or no economic and/or performance impact


Production concentration

The percentage of an element produced in the top producing country. The higher the value, the larger risk there is to supply.


Reserve distribution

The percentage of the world reserves located in the country with the largest reserves. The higher the value, the larger risk there is to supply.


Political stability of top producer

A percentile rank for the political stability of the top producing country, derived from World Bank governance indicators.


Political stability of top reserve holder

A percentile rank for the political stability of the country with the largest reserves, derived from World Bank governance indicators.


Supply risk

 
Relative supply risk 8.6
Crustal abundance (ppm) 0.8
Recycling rate (%) 10–30
Substitutability High
Production concentration (%) 40
Reserve distribution (%) 43
Top 3 producers
  • 1) China
  • 2) USA
  • 3) Chile
Top 3 reserve holders
  • 1) China
  • 2) USA
  • 3) Chile
Political stability of top producer 24.1
Political stability of top reserve holder 24.1
 

Glossary


Common oxidation states

The oxidation state of an atom is a measure of the degree of oxidation of an atom. It is defined as being the charge that an atom would have if all bonds were ionic. Uncombined elements have an oxidation state of 0. The sum of the oxidation states within a compound or ion must equal the overall charge.


Isotopes

Atoms of the same element with different numbers of neutrons.


Key for isotopes


Half life
  y years
  d days
  h hours
  m minutes
  s seconds
Mode of decay
  α alpha particle emission
  β negative beta (electron) emission
  β+ positron emission
  EC orbital electron capture
  sf spontaneous fission
  ββ double beta emission
  ECEC double orbital electron capture

Oxidation states and isotopes

 
Common oxidation states 6, 5, 4, 3, 2, 0
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  92Mo 91.907 14.77 > 3 x 1017 β+-EC 
  94Mo 93.905 9.23
  95Mo 94.906 15.9
  96Mo 95.905 16.68
  97Mo 96.906 9.56
  98Mo 97.905 24.19
  100Mo 99.907 9.67 6 x 1020 β-β- 
 

Glossary


Specific heat capacity (J kg−1 K−1)

Specific heat capacity is the amount of energy needed to change the temperature of a kilogram of a substance by 1 K.


Young's modulus

A measure of the stiffness of a substance. It provides a measure of how difficult it is to extend a material, with a value given by the ratio of tensile strength to tensile strain.


Shear modulus

A measure of how difficult it is to deform a material. It is given by the ratio of the shear stress to the shear strain.


Bulk modulus

A measure of how difficult it is to compress a substance. It is given by the ratio of the pressure on a body to the fractional decrease in volume.


Vapour pressure

A measure of the propensity of a substance to evaporate. It is defined as the equilibrium pressure exerted by the gas produced above a substance in a closed system.

Pressure and temperature data – advanced

 
Specific heat capacity
(J kg−1 K−1)
251 Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) 231
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - - - - - 1.83
x 10-9
4.07
x 10-7
3.03
x 10-5
0.00102 0.0189
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History

The soft black mineral molybdenite (molybdenum sulfide, MoS2), looks very like graphite and was assumed to be a lead ore until 1778 when Carl Scheele analysed it and showed it was neither lead nor graphite, although he didn’t identify it.

Others speculated that it contained a new element but it proved difficult to reduce it to a metal. It could be converted to an oxide which, when added to water, formed an acid we now know as molybdic acid, H2MoO4, but the metal itself remained elusive.

Scheele passed the problem over to Peter Jacob Hjelm. He ground molybdic acid and carbon together in linseed oil to form a paste, heated this to red heat in and produced molybdenum metal. The new element was announced in the autumn of 1781.
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Podcasts

Listen to Molybdenum Podcast
Transcript :

Chemistry in its element: molybdenum


Promo)

You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry.

(End promo)

Meera Senthilingam

This week, we clarify the importance of the often misunderstood molybdenum. Here's Quentin Cooper:

Quentin Cooper

The answer to the ultimate question - of life, the Universe and Everything - is, as every Douglas Adams fan knows, 42. And 42, as every Mendeleev fan knows, is the atomic number of molybdenum. And for many that - plus the indisputable fact that molybdenum is a funny word - is often about as far as their knowledge goes of this silvery metal - not that they'd have known it was a silvery metal - which is wedged between its better known brethren chromium and tungsten in group six of the periodic table. That odd-sounding name comes in a convoluted way from the Greek for lead, as ores of the two were often mixed up by early mineralogists - it was also frequently mistaken for graphite - and it wasn't until 1778 that molybdenum was recognised as a distinct entity deserving its own place in the periodic table, and a few years later still that it was finally isolated. The key breakthrough came from the Swedish chemist Carl Wilhlelm Scheele, better known as 'Hard luck Scheele' because he made a whole series of chemical discoveries, including oxygen, only for others to go and get the credit.

So its mistaken-identity history, its miscredited discoverer, its misleading and often mis-spelled name, all add to the aura of comedy and confusion around molybdenum.....and yet it's an element that's right at the root of life - not just human life, but pretty much all life on the planet: yes you'll find tiny amounts of it in everything from the filaments of electric heaters to missiles to protective coatings in boilers, and its high performance at high temperatures mean it has a range of commercial applications: it's useful in toughening up steel and giving it more corrosion resistance, as a catalyst in processes such as refining petroleum, and above all it's turned to when you need things to get hot but stay slippy - where WD40 and other petroleum derived oils are at risk of igniting, molybdenum sulfides are the basis of a range of lubricants which can cope with the heat and keep things moving smoothly.

But for all the ways we've discovered to use it, of far greater significance - although involving far smaller quantities of molybdenum - is the way we've evolved to make use of it within us. It's found in dozens of enzymes... including all important nitrogenase, which allows the most abundant element in the atmosphere, nitrogen, to be taken up and turned into compounds that enable bacteria, plants, us and everything between to synthesise and utilise proteins. Without proteins there wouldn't be much at all in the way of life....and without molybdenum there wouldn't be much at all in the way of proteins. And it turns up in other key human enzymes too such as xanthine oxidase in the liver, which is vital to our waste processing.

But just in case anyone's thinking of rushing off to buy one of the many commercially available trace mineral supplements with molybdenum it's worth adding that although like much of life on Earth we definitely need it.... we don't need that much of it: about a third of a gram is all you'll get through in an entire lifetime. That's next to nothing...but without it we'd be next to nothingness.

So, time to stop laughing at the funny name... molybdenum really is one of life's few true essentials.

Meera Senthilingham

So time to give some much-owed respect, it seems, to the element molybdenum. That was science broadcaster Quentin Cooper with the widely applied chemistry of molybdenum. Now, next week, blink and you may miss it.

Brian Clegg

If elements were insects, darmstadtium would be the mayfly of the chemical world. It exists for the most fleeting time before it transforms to something else. Darmstadium is never going to have a practical use - but its sheer brevity of existence gives it a wistful fascination.

Meera Senthilingham

And to find out what does happen in darmstadtium's brief existence on earth, in next week's Chemistry in its element. Until then, I'm Meera Senthilingham and thank you for listening.

(Promo)

Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by thenakedscientists.com. There's more information and other episodes of Chemistry in its element on our website at chemistryworld.org/elements.

(End promo)
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  Help Text

Resources

Description :
In this experiment you will be looking at a group of transition elements chromium, molybdenum and tungsten.
Description :
A collection of visually stimulating and informative infographics about the elements, which would make a valuable addition to any science classroom.
Description :
Assessment for Learning is an effective way of actively involving students in their learning. This is a series of plans based around chemistry topics.
Description :
When concentrated hydrochloric acid is added to a very dilute solution of copper sulfate, the pale blue solution slowly turns yellow-green on the formation of a copper chloride complex. When concentr...
Description :
The purpose of this experiment is to observe and interpret some of the chemistry of three first row transition elements and to compare them with a typical s-block element.
Description :
The periodic table allows chemists to see similarities and trends in the properties of chemical elements. This experiment illustrates some properties of the common transition elements and their compou...
 

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References

 
Visual Elements images and videos
© Murray Robertson 2011.

 

Data

W. M. Haynes, ed., CRC Handbook of Chemistry and Physics, CRC Press/Taylor and Francis, Boca Raton, FL, 95th Edition, Internet Version 2015, accessed December 2014.
Tables of Physical & Chemical Constants, Kaye & Laby Online, 16th edition, 1995. Version 1.0 (2005), accessed December 2014.
J. S. Coursey, D. J. Schwab, J.J. Tsai, and R. A. Dragoset, Atomic Weights and Isotopic Compositions(version 3.0), 2010, National Institute of Standards and Technology, Gaithersburg, MD, accessed December 2014.
T. L. Cottrell, The Strengths of Chemical Bonds, Butterworth, London, 1954.

 

Uses and properties

John Emsley, Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, New York, 2nd Edition, 2011.
Thomas Jefferson National Accelerator Facility - Office of Science Education, It’s Elemental - The Periodic Table of Elements, accessed December 2014.
Periodic Table of Videos, accessed December 2014.

 

Supply risk data

Derived in part from material provided by the British Geological Survey © NERC.

 

History text

© John Emsley 2012.

 

Podcasts

Produced by The Naked Scientists.

 

Periodic Table of Videos

Created by video journalist Brady Haran working with chemists at The University of Nottingham.